1. Field of the Invention
The present invention relates to a method for driving a plasma display panel, and more particularly, to a method for driving a three-electrode surface-discharge plasma display panel.
2. Description of the Related Art
FIG. 1 shows a structure of a general three-electrode surface-discharge plasma display panel, FIG. 2 shows an electrode line pattern of the panel shown in FIG. 1, and FIG. 3 shows an example of a pixel of the panel shown in FIG. 1. Referring to the drawings, address electrode lines A.sub.1, A.sub.2, . . . A.sub.m, dielectric layers 11 and 15, Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n, X electrode lines X.sub.1, X.sub.2, . . . , and X.sub.n, phosphors 16, partition walls 17 and a MgO protective film 12 are provided between front and rear glass substrates 10 and 13 of a general surface-discharge plasma display panel 1.
The address electrode lines A.sub.1, A.sub.2, . . . A.sub.m coat the front surface of the rear glass substrate 13 in a predetermined pattern. The lower dielectric layer 15 entirely coats the front surface of the address electrode lines A.sub.1, A.sub.2, . . . A.sub.m. The partition walls 17 on the front surface of the lower dielectric layer 15 are parallel to the address electrode lines A.sub.1, A.sub.2, . . . A.sub.m. The partition walls 17 define discharge areas of the respective pixels and prevent optical crosstalk among pixels. The phosphors 17 coatings are between partition walls 17.
The X electrode lines X.sub.1, X.sub.2, . . . X.sub.n and the Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n are arranged on the rear surface of the front glass substrate 10 orthogonal to the address electrode lines A.sub.1, A.sub.2, . . . A.sub.m in a predetermined pattern. The respective intersections define corresponding pixels. The X electrode lines X.sub.1, X.sub.2, . . . and X.sub.n and the Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n are each comprised of conductive indium tin oxide (ITO) electrode lines (X.sub.na and Y.sub.na of FIG. 3) and metal bus electrode lines (X.sub.nb and Y.sub.nb of FIG. 3). The upper dielectric layer 11 entirely coats the rear surface of the X electrode lines X.sub.1, X.sub.2, . . . X.sub.n and the Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n. The MgO protective film 12 for protecting the panel 1 against strong electrical fields entirely coats the rear surface of the upper dielectric layer 11. A gas for forming plasma is hermetically sealed in a discharge space 14.
The above-described plasma display panel is basically driven such that a reset step, an address step and a sustain-discharge step are sequentially performed in a unit subfield. In the reset step, wall charges remaining in the previous subfield are erased and space charges are evenly formed. In the address step, the wall charges are formed in a selected pixel area. Also, in the sustain-discharge step, light is produced at the pixel at which the wall charges are formed in the address step. In other words, if alternating pulses of a relatively high voltage are applied between the X electrode lines X.sub.1, X.sub.2, . . . X.sub.n, and the Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n, a surface discharge occurs at the pixels at which the wall charges are formed. Here, plasma is formed at the gas layer of the discharge space 14 and the phosphors 142 are excited by ultraviolet rays to thus emit light.
FIG. 4 shows a unit frame for displaying gray scales on the plasma display panel shown in FIG. 1 according to the general sequential driving method. Here, a unit display period represents a frame in the case of a progressive scanning method, and a field in the case of an interlaced scanning method. The driving method shown in FIG. 4 is generally referred to as a multiple address overlapping display driving method. According to this driving method, pulses for a display discharge are consistently applied to all X electrode lines X.sub.1, X.sub.2, . . . X.sub.n and all Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n, and pulses for resetting or addressing are applied between the respective pulses for a display discharge. Here, the pulses for resetting or addressing are applied to the Y electrode lines corresponding to a plurality of subfields SF.sub.1, SF.sub.2, . . . SF.sub.8 set as driving periods for the purpose of displaying gray scales in a time-divisional manner.
Thus, compared to an address-display separation driving method, the multiple address overlapping display driving method has an enhanced displayed luminance. Here, the address-display separation driving method refers to a method in which within a unit subfield, reset and address steps are performed for all Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.n, during a certain period and a display discharge step is then performed.
Referring to FIG. 4, a unit field or frame is divided into 8 subfields SF.sub.1, SF.sub.2, . . . SF.sub.8 for achieving a time-division gray scale display. Also, in each subfield, reset, address and sustain-discharge steps are performed, and the time allocated to each sub-field is determined by the display discharge time corresponding to gray scales. For example, in the case of displaying 256 gray scales with 8-bit image data in units of frames, assuming that a unit frame, generally 1/60 sec, consists of 256 unit times, the first subfield SF.sub.1 driven by the image data of the least significant bit has 1 (2.sup.0) unit time, the second subfield SF.sub.2 2 (2.sup.1) unit times, the third subfield SF.sub.3 4 (2.sup.2) unit times, the fourth subfield SF.sub.4 8 (2.sup.3) unit times, the fifth subfield SF.sub.5 16 (2.sup.4) unit times, the sixth subfield SF.sub.6 32 (2.sup.5) unit times, the seventh subfield SF.sub.7 64 (2.sup.6) unit times, and the eighth subfield SF.sub.8 driven by the image data of the most significant bit 128 (2.sup.7) unit time, respectively. In other words, since the sum of the unit times allocated to the respective subfields is 255 unit times, it is possible to achieve 255 gray scale display, and 256 gray scale display inclusive of one gray scale in which a no display discharge occurs in any subfield.
If an address step is performed for a Y electrode line and then a display discharge step is performed in the first subfield SF.sub.1, an address step is performed for the corresponding Y electrode line at the second subfield SF.sub.2. The same procedure is applied to subsequent subfields SF.sub.3, SF.sub.4, . . . SF.sub.8. For example, if an address step is performed for a corresponding Y electrode line and then a display discharge step is performed in the seventh subfield SF.sub.7, an address step is performed for the corresponding Y electrode line at the eighth subfield SF.sub.8. Although the time for a unit subfield equals the time for a unit field or frame, the respective unit subfields are overlapped on the basis of driven Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.480 to form a unit field or frame. Thus, since all subfields SF.sub.1, SF.sub.2, . . . SF.sub.8 exist at every timing, time slots for addressing, depending on the number of subfields, are set between the respective display discharge pulses for the purpose of performing the respective address steps.
FIG. 5 shows driving signals in a unit field or frame based on the driving method shown in FIG. 4. In FIG. 5, S.sub.y1, S.sub.y2, . . . S.sub.y8 denote driving signals applied to the corresponding Y electrode lines of the respective subfields. In more detail, S.sub.y1 denotes a driving signal applied to a Y electrode line of the first subfield (SF.sub.1 of FIG. 4), S.sub.y2 a driving signal applied to a Y electrode line of the second subfield (SF.sub.2 of FIG. 4), S.sub.y3 a driving signal applied to a Y electrode line of the third subfield (SF.sub.3 of FIG. 4), S.sub.y4 a driving signal applied to a Y electrode line of the fourth subfield (SF.sub.4 of FIG. 4), S.sub.y5 a driving signal applied to a Y electrode line of the fifth subfield (SF.sub.5 of FIG. 4), S.sub.y6 a driving signal applied to a Y electrode line of the sixth subfield (SF.sub.6 of FIG. 4), S.sub.y7 a driving signal applied to a Y electrode line of the seventh subfield (SF.sub.7 of FIG. 4), and S.sub.y8 a driving signal applied to a Y electrode line of the eighth subfield (SF.sub.8 of FIG. 4), respectively. S.sub.X1 . . . 4 and S.sub.X5 . . . 8 denote driving signals applied to X electrode line groups corresponding to scanned Y electrode lines, S.sub.A1 . . . m denotes display data signals applied to all address electrode lines (A.sub.1, A.sub.2, . . . A.sub.m of FIG. 1), and GND denotes a ground voltage.
FIG. 6 shows in more detail driving signals S.sub.y1, S.sub.y2, . . . S.sub.y8 applied to the corresponding Y electrode lines of the respective subfields in time periods T.sub.31 to T.sub.42 shown in FIG. 5.
Referring to FIGS. 5 and 6, pulses 2 and 5 for a display discharge are consistently applied to all X electrode lines (X.sub.1, X.sub.2, . . . X.sub.n of FIG. 1) and all Y electrode lines Y.sub.1, Y.sub.2, . . . Y.sub.480, and a reset pulse 3 or a scan pulse 6 are applied between the respective pulses 2 and 5 for a display discharge. Here, the pulses for resetting or addressing are applied to the Y electrode lines corresponding to a plurality of subfields SF.sub.1, SF.sub.2, . . . SF.sub.8.
There exists a predetermined quiescent period until the scan pulse 6 is applied since the reset pulse 3 was applied, so that space charges are smoothly distributed at the corresponding pixel areas. In FIG. 5, time periods T.sub.12, T.sub.21, T.sub.22 and T.sub.31 denote quiescent periods corresponding to Y electrode line groups of the first through fourth subfields, and time periods T.sub.22, T.sub.31, T.sub.32 and T.sub.41 denote quiescent periods corresponding to Y electrode line groups of the fifth through eighth subfields. The pulses 5 for a display discharge applied during the respective quiescent periods cannot actually cause a display discharge but allow space charges to be smoothly distributed at the corresponding pixel areas. However, the pulses 2 for a display discharge applied during periods other than the quiescent periods cause a display discharge at the pixels where wall charges have been formed by the scan pulse 6 and the display data signal S.sub.A1 . . . m.
Between the last pulses, among the pulses 5 for a display discharge applied during the quiescent periods, and the first pulses 2 for a display discharge, subsequent to the last pulses, addressing is performed four times. For example, addressing is performed for the Y electrode line group corresponding to the first through fourth subfields during a time period T.sub.32. Also, addressing is performed for the Y electrode line group corresponding to the fifth through eighth subfields during a time period T.sub.42. As described above with reference to FIG. 4, since all subfields SF.sub.1, SF.sub.2, . . . SF.sub.8 exist at every timing, time slots for addressing, depending on the number of subfields, are set between the respective pulses for a display discharge for the purpose of performing the respective address steps.
In the method for driving the 3-electrode surface discharge plasma display panel, conventionally, the scanning order of a plurality of subfields is constant, irrespective of the display period. For example, in the first subfield SF.sub.1 and the fifth subfield SF.sub.5, scanning is always done at the first time slot. Also, in the second subfield SF.sub.2 and the sixth subfield SF.sub.6, scanning is always done at the second time slot. Likewise, in the third subfield SF.sub.3 and the seventh subfield SF.sub.7, scanning is always done at the third time slot. In the fourth subfield SF.sub.4 and the eighth subfield SF.sub.8, scanning is always done at the fourth time slot.
However, the standby times required for wall charges which have been formed on the respective Y electrode lines by addressing to wait for the pulses (T.sub.31 of FIG. 5 or 2 in the time period T.sub.41) are different. As the standby time becomes longer, much more wall charges which have been formed at the pixels to be displayed are lost. According to the conventional driving method, it is quite highly probable that pixels to be displayed at subfields having the first scanning time slot, for example, the first subfield SF.sub.1 and the fifth subfield SF.sub.5, are consistently displayed. Thus, uniformity and stability of a display may be deteriorated.